Athermal arrayed waveguide grating

ABSTRACT

An athermal arrayed-waveguide grating is disclosed and includes an input waveguide for inputting two or more optical signals from one exterior side, a grating array for separating the optical signals into different wavelengths of light, a first slab, formed with two layers and having different refractive indices from each other, for connecting the input waveguide with the grating array, a second slab for causing the different light wavelengths separated at the grating array to be imaged on an egress surface thereof, and an output waveguide array for outputting each light wavelength imaged on the egress surface of the second slab to the other exterior side in the form of a separated channel.

CLAIM OF PRIORITY

[0001] This application claims priority to an application entitled“Athermal arrayed waveguide grating,” filed in the Korean IntellectualProperty Office on Jan. 21, 2003 and assigned Serial No. 2003-4028, thecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an athermal arrayed waveguidegrating and, more particularly, to an arrayed waveguide grating capableof compensating wavelength changes according to variations in ambienttemperature.

[0004] 2. Description of the Related Art

[0005] With a recent burst of growth of various data services in theInternet field, there has been an increase in demand for highertransmission capacity. The current demand does not seem to slow down inany foreseeable future. The best economical plan of meeting this demandis to maximize the transmission capacity in the existing optical fibers.For example, an optical communication system is operated in awavelength-division-multiplexing (WDM) mode in which a plurality ofchannels can be transmitted/received through a single optical fiber asone communication line, instead of installing additional optical fiberson a large scale. This type of optical-communication system wascommercialized in 1995 for the first time, and since then the availabletransmission/reception capacity has been improved remarkably.

[0006] In the WDM systems, an optical device, such as an arrayedwaveguide grating in which an optical waveguide is formed on a flatplate of silica by a combination of fiber optic technology with alarge-scale-integrated (LSI) circuit technique, is used as awavelength-division multiplexer/demultiplexer for allowing multiplewavelengths to be combined and separated for transmission/receptionapplications. However, the arrayed waveguide grating is sensitive totemperature change which in turn changes its refractive index accordingto the temperature changes. As a result, optical signals inputted intothe arrayed-waveguide grating are subjected to a change in the phase,thereby causing a wavelength sweep.

[0007] In general, the arrayed-waveguide grating (AWG) includes an inputwaveguide, a grating array, first and second slabs, and an outputwaveguide array, and functions as a wavelength-divisionmultiplexer/demultiplexer in which optical signals inputted from theoutside are not only demultiplexed into a plurality of channels havingdifferent wavelengths but also multiplexed into one channel, and thenoutputs the multiplexed/demultiplexed resultant(s). The AWG may furtherinclude a temperature controller, thus preventing a wavelength sweep ofoutputted channel(s) caused by a change in ambient temperature. Thetemperature controller typically includes a heater device or a peltierdevice. An isothermal plate of copper, for instance, may also beinserted between the AWG and a heater or peltier device.

[0008] In operation, the input waveguide inputs external optical signalsinto the first slab. The grating array separates the inputted opticalsignals into different light wavelengths. The first slab connects theinput waveguide with the grating array. Meanwhile, the second slaballows the separated wavelengths of light to be imaged on its egresssurface. Further, the output-waveguide array allows each wavelength oflight, which is imaged on the egress surface of the second slab, to beoutputted to the outside in the form of a separated channel.

[0009] The AWG or waveguide module including the heater or peltierdevice as mentioned above is disclosed in the International PatentApplication No. PCT/JP2001/00352 to Hiro Yoshiyuki, et al., entitled“Heater Module and Optical Waveguide Module,” the teachings of which arehereby incorporated by reference.

[0010] Briefly, the AWG includes the temperature controller, so that theAWG suppresses a change in the phase of an optical signal caused by thetemperature change as well as the wavelength sweep of each outputchannel. That is to say, the temperature controller allows the AWG tomaintain a constant temperature, so that each output channel can beprevented from being swept in wavelength, thereby enabling the AWG toobtain a stable performance characteristic. However, because theconventional AWG employs a heater or peltier device as the temperaturecontroller, the AWG must be always heated during operation. As a result,a power consumption for the AWG is increased. In addition, there areother drawbacks in that the prior art AWG which includes an increasedvolume, a complicated assembly process, an increased manufacturing cost,and so forth.

[0011] Accordingly, there is a need for an improved arrayed waveguidegrating that is not sensitive to variations in ambient temperature thatmay be realized in a simple, reliable, and inexpensive implementation.

SUMMARY OF THE INVENTION

[0012] The present invention is related to an athermal arrayed waveguidegrating capable of reducing power consumption and volume while enhancingthe production efficiency.

[0013] In one embodiment, an athermal arrayed waveguide grating isprovided and includes: an input waveguide for inputting two or moreoptical signals from one exterior side; a grating array for separatingthe optical signals into different wavelengths of light; a first slab,formed with two layers and having different refractive indices from eachother, for connecting the input waveguide with the grating array; asecond slab for causing the different wavelengths of light separated atthe grating array to be imaged on an egress surface thereof; and, anoutput waveguide array for outputting each wavelength of light imaged onthe egress surface of the second slab to the other exterior side in theform of a separated channel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above features and advantages of the present invention willbe more apparent from the following detailed description taken inconjunction with the accompanying drawings, in which:

[0015]FIG. 1 is a perspective view showing an arrayed waveguide grating(AWG) according to an embodiment of the present invention; and,

[0016]FIG. 2 is an enlarged plan view of portions of the input waveguideand the first slab shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Hereinafter, a preferred embodiment of the present invention willbe described in detail with reference to the accompanying drawings. Forthe purposes of clarity and simplicity, a detailed description of knownfunctions and configurations incorporated herein will be omitted as itmay make the subject matter of the present invention unclear.

[0018]FIG. 1 is a perspective view showing an arrayed-waveguide grating(AWG) according to an embodiment of the present invention. As shown, theAWG comprises an optical layer 120 having a core layer and a clad layerand deposited on a substrate 110 of silica, an input waveguide 130, afirst slab 140, a grating array 150, a second slab 160, and an outputwaveguide 170 formed on the optical layer 120. The input waveguide 130serves to cause input optical signals to be inputted into the first slab140, in which each optical signal has a preset wavelength range.

[0019]FIG. 2 is an enlarged view of the input waveguide 130 and thefirst slab 140 shown in FIG. 1. As shown in FIG. 2, the first slab 140is operative to connect the input waveguide 130 with the grating array150. The first slab 140 comprises first and second layers 141 and 142having different refractive indices n1 and n2, wherein the first layer141 has a different refractive index n2 than the input waveguide 130,and the second layer 142 has the same refractive index n1 as that of theinput waveguide 130.

[0020] The input waveguide 130 is made up of a medium having the samerefractive index n1 as that of the second layer 142, and is bounded onone side by the first layer 141. As such, an optical signal is incidenton the input waveguide 130 at a predetermined incident angle α.

[0021] The first layer 141 has a different refractive index n2 from thatof the second layer 142 or the input waveguide 130. Therefore, anoptical signal incident from the input waveguide 130 to the first layer141 at an incident angle α is refracted at a predetermined refractiveangle β. Note that the relationship among the refractive angle β of theoptical signal refracted at the first layer 141, the refractive index ofthe first layer 141, the incident angle α of the optical signaltraveling through the input waveguide 130, and the refractive index ofthe input waveguide 130 follows Equation 1 according to Snell's law, asfollows.

n₁ sin α=n₂ sin β,  Equation 1

[0022] where n1 represents the refractive index of the input waveguide130, a represents the incident angle of the optical signal travelingthrough the input waveguide 130, n2 represents the refractive index ofthe first layer 141, and P represents the refractive angle of theoptical signal refracted in the first layer 141.

[0023] The second layer 142 has a refractive index that is differentfrom the first layer 141 but is equal to that of the input waveguide130. Accordingly, the optical signal incident from the first layer 141to the second layer 142 is refracted at a predetermined refractive angleα owing to a refractive index difference between the first and secondlayers 141 and 142. To be more specific, because the input waveguide 130has the same refractive index as the second layer 142, the opticalsignal which passes through the first layer 141 and then enters thesecond layer 142 has the refractive angle α of the same gradient as thatof the incident angle α of the optical signal which travels through theinput waveguide 130.

[0024] Note that with a change in temperature, the refractive index ofthe first layer 141 varies. As a result, the optical signal incident onthe first layer 141 is subjected to a refraction at a differentrefractive angle γ from the original refractive angel β. However, thesecond layer 142 has the same refractive index n1 as that of the inputwaveguide 130, so that the optical signal incident on the second layer142 is refracted at a refractive angle α which is equal to the incidentangle α of the optical signal incident on the input waveguide 130.

[0025] As noted before, due to the change in external temperature, theoptical signal traveling through the first layer 141 undergoes a changein its refractive angle γ. However, an optical path of the opticalsignal within the first slab 140 is transformed depending the degree ofambient-temperature changes. Regardless, the second layer 142compensates for a change in the wavelength caused by the temperaturechange by reconverging the optical signal inputted from the first layer141. The refractive index of the first layer 141 depending on thetemperature change is changed differently compared with that of thesecond layer 142, and thereby the wavelength sweep resulting from thetemperature change of the optical signal is corrected. Note that ifdn/dT of material determining n2 and an incident angle are set to beindependent from the temperature at a first slap constructed after theinitial temperature condition is determined, the wavelength of an outputunit at different temperature is not change.

[0026] The first slab according to the present invention may beconstructed, for instance, so that the first layer 141 has a refractiveindex of 1.415 and a length of 21.07 μm in a direction in which theoptical signal travels, and the second layer 142 has a refractive indexof 1.46. In this case, an initial optical signal, which is inputted intothe first slab 140 before the temperature is changed, allows the opticalsignal to have an incident angle α of 30° when it is incident on thefirst layer 141, and a refractive angle α of 30° when it travels throughthe second layer 142. Further, the optical signal traveling through thefirst layer 141 has a refractive angle β of 31.03° when the temperatureis not changed, but a refractive angle γ of 30.5° when the temperatureis changed. Accordingly, the refractive index of the first layer 141 hasa change rate of about 0.025 per 1° C.

[0027] Referring back to FIG. 1, the grating array 150 comprises aplurality of waveguides having a different length from each other. Theoptical signals inputted from the first slab 140 are separated intodifferent light wavelengths due to a length difference between thewaveguides and are outputted to the second slab 160.

[0028] The second slab 160 receives the different light wavelengthsseparated by the grating array 150, and then causes the received lightto be imaged on its egress surface. The output-waveguide array 170 isconnected to the output side of the second slab 160 and functions as apassage for outputting each light imaged on the egress surface of thesecond slab 160 to the outside in the form of a separated channel, inwhich the separated channels λ1 to λn have different wavelengths fromeach other.

[0029] As can be seen from the above, the AWG according to the presentinvention is formed with the first slab having different refractiveindices from each other, so that it can compensate a wavelength sweepcaused by a change in temperature without the conventional heater orpeltier device. Therefore, the athermal arrayed-waveguide gratingaccording to the present invention makes it possible to reduce itsvolume and manufacturing process.

What is claimed is:
 1. An athermal arrayed-waveguide grating comprising:an input waveguide for inputting two or more optical signals; a gratingarray for separating the input optical signals into different lightwavelengths; a first slab having a first layer and a second layer withdifferent refractive indices from each other for coupling the inputwaveguide with the grating array; a second slab for causing thedifferent light wavelengths separated at the grating array to be imagedon an egress surface thereof; and, an output-waveguide array foroutputting each light wavelength imaged on the egress surface of thesecond slab in a form of a separated channel.
 2. An athermalarrayed-waveguide grating according to claim 1, wherein the first layerconnected to the input waveguide comprises a predetermined refractiveindex that is different from the input waveguide.
 3. An athermalarrayed-waveguide grating according to claim 1, wherein the second layerinterposed between the first layer and the grating array comprises arefractive index that is equal to that of the input waveguide.
 4. Anathermal arrayed-waveguide grating according to claim 2, wherein thefirst layer is formed by material having a refractive index of 1.415. 5.An athermal arrayed-waveguide grating according to claim 2, wherein thesecond layer is formed by material having a refractive index of 1.46. 6.An athermal arrayed-waveguide grating according to claim 2, wherein thefirst layer of the first slab has a length of 21.07 μm in a direction inwhich the optical signal travels.
 7. An optical-waveguide device forguiding an optical signal comprising: a substrate; an input waveguideextending at least partially across the substrate, a grating array forseparating the optical signals into different light wavelengths; a fistslab having a first layer and a second layer for coupling the gratingarray with the input waveguide; and, a second slab for coupling thedifferent light wavelengths separated by the grating array to an outputwaveguide, where the reflective index of the first layer and the secondlayer is substantially different.
 8. An optical-waveguide device ofclaim 7, wherein the reflective index of the second layer is the same asthe input waveguide.
 9. An optical-waveguide device of claim 7, whereinthe input and output waveguides extend at least partially across thesubstrate.
 10. An optical-waveguide device of claim 7, wherein thegrating array extend at least partially across the substrate.
 11. Anoptical-waveguide device of claim 7, wherein the first layer is formedby material having a refractive index of 1.415.
 12. An optical-waveguidedevice of claim 7, wherein the second layer is formed by material havinga refractive index of 1.46.
 13. An optical-waveguide device of claim 7,wherein the first layer of the first slab has a length of 21.07 μm in adirection in which the optical signal travels.
 14. A method ofmanufacturing an optical-waveguide device for guiding an optical signal,the method comprising steps of: forming an input waveguide extending atleast partially across the substrate; forming a first slab having afirst layer and a second layer extending at one end of the inputwaveguide, the first layer having a first reflective index value and thesecond layer having a second reflective index value; forming a gratingarray extending at one end of the first slab and extending at leastpartially across the substrate; and, forming a second slab extending atone end of the grating array and extending at least partially across thesubstrate.
 15. The method of claim 14, further comprising the step offorming an output waveguide extending at one end of the second slab andextending at least partially across the substrate.
 16. The method ofclaim 14, wherein the reflective index of the second layer is formed bythe same reflective index of the input waveguide.
 17. The method ofclaim 14, wherein the first layer is formed by material having arefractive index of 1.415.
 18. The method of claim 14, wherein thesecond layer is formed by material having a refractive index of 1.46.19. The method of claim 14, the first layer of the first slab has alength of 21.07 μm in a direction in which the optical signal travels.